The present invention relates to methods for carrying out the dry cleaning of fabrics (e.g., garments) in liquid carbon dioxide, and particularly relates to methods and apparatus for adding detergent formulations to liquid carbon dioxide dry cleaning systems.
Many traditional solvent-based cleaning applications can suffer from poor performance on aqueous born soils. A significant portion of the soils found in conventional dry cleaning can be categorized as partially or wholly water-soluble. Water-in-oil surfactants have been developed that effectively disperse water to yield optically clear homogeneous mixtures. These dispersions can effectively dissolve water-soluble soils, termed secondary solublization, if the proper water activity is achieved in a given cleaning solvent. Water activity, determined by a number of factors including temperature, the nature of solvent-solute interactions and the molar ratio of surfactant to water, is generally monitored in conventional dry cleaning by what is termed as relative humidity. A cleaning bath with low relative humidity and hence low water activity will not allow for secondary solublization of aqueous born soils. Water exceeding a critical level can lead to non-dispersed bulk water that can be deleterious to certain garment types.
Carbon dioxide based dry cleaning is a new technology that has only recently been commercially implemented. Like conventional dry cleaning solvents watersoluble soils are not inherently soluble in liquefied carbon dioxide. Surfactant systems that enable the water bearing nature of liquid carbon dioxide have been disclosed in the patent and open literature. Under certain conditions these systems have demonstrated that water-soluble materials can be dissolved and dispersed in a liquid carbon dioxide medium.
Many conventionally used water-in-oil surfactants applied to dry cleaning solvents are not compatible with liquid CO2 solvent systems. Surfactants containing what is termed to be xe2x80x9cCO2-philicxe2x80x9d function have been proven to be useful in the emulsification of water in CO2. The exclusive use of some of these materials can be cost prohibitive for many applications. The case for dissolution of water-soluble materials in CO2 can be further complicated by the reversible reaction between water a and carbon dioxide producing carbonic acid. This weak acid which reverts back to water and carbon dioxide as pressure is lowered and CO2 is removed can have substantial implications on water activity in CO2. Lower water activity can effect the ability of the CO2 cleaning fluid to dissolve water-soluble soils. Certain pH buffers have been used in liquid and supercritical CO2 to control the pH of aqueous micro and macro-domains and in turn augment water activity. Attempts to raise the water activity in current processes by the addition of bulk water can fail because of the inability of the CO2 and surfactant combinations to sufficiently stabilize the water. Bulk water phase-separated from liquid CO2 cleaning fluids and conventional cleaning fluids can have substantial detrimental effects on many dry clean only fabrics.
Not all stains are water soluble. Indeed, a significant number of stains that must be cleaned in a dry cleaning operation are hydrophobic. Thus, in addition to aqueous detergent formulations, it is also desirable to have a means for adding low water content detergent formulations to carbon dioxide dry cleaning systems.
U.S. Pat. No. 5,858,022 to Romack et al. and U.S. Pat. No. 5,683,473 to Jureller et al. (see also U.S. Pat. No. 5,683,977 to Jureller et al.) describe carbon dioxide dry cleaning methods and compositions. Our co-pending U.S. Pat. application Ser. No. 09/047,013 of McClain et al., filed Mar. 24, 1998, describes carbon dioxide dry cleaning apparatus. Dry cleaning apparatus is also described in U.S. Pat. Nos. 5,467,492 to Chao et al., 5,651,276 to Purer et al., and 5,784,905 to Townsend et al. It will be seen that there is a need for better ways to add detergent formulations to the carbon dioxide during operation of the apparatus.
A first aspect of the present invention is system for the controlled addition of detergent formulations and the like to a carbon dioxide cleaning apparatus. The system preferably comprises:
(a) a high pressure wash vessel;
(b) an auxiliary vessel;
(c) a drain line connecting the auxiliary vessel to the wash vessel;
(d) optionally but preferably, a separate vent line connecting the auxiliary vessel to the wash vessel;
(e) a detergent reservoir; and
(f) a detergent supply line connecting the detergent reservoir to the auxiliary vessel.
An advantage of this apparatus is that, because the detergent formulation can be pumped into the auxiliary vessel in a predetermined aliquot or amount, which predetermined aliquot or amount can then be transferred into the wash vessel where it combines with the liquid carbon dioxide cleaning solution, the detergent formulation can be added to the cleaning solution in a more controlled or accurate manner.
A second aspect of the present invention is a method for the controlled addition of a low-water content detergent formulation or the like (e.g., a starch or size formulation) to a carbon dioxide dry cleaning system. The method comprises:
(a) providing a carbon dioxide cleaning apparatus comprising a wash vessel and a separate auxiliary vessel;
(b) reducing the pressure in the wash vessel and the auxiliary vessel; then
(c) adding a detergent formulation to the auxiliary vessel, the detergent (c) formulation comprising (i) at least 30 percent organic co-solvent, (ii) at least 1 percent surfactant; and (ii) not more than 10 percent water (and preferably less than 10 percent water); then
(d) increasing the pressure in the wash vessel so that liquid carbon dioxide can be pumped therethrough to clean articles in the wash vessel; and then
(e) transferring the detergent formulation from the auxiliary vessel to the wash vessel to facilitate the cleaning of articles therein.
A third aspect of the present invention is a system for the addition of aqueous detergent formulations and the like to a carbon dioxide dry cleaning system under turbulent conditions. The system preferably comprises:
(a) a high pressure wash vessel;
(b) a filter;
(c) a carbon dioxide cleaning solution drain line interconnecting the wash vessel to the filter;
(d) a carbon dioxide cleaning solution supply line connecting the filter to the wash vessel;
(e) a first high pressure pump (i.e., a pump that is capable of pumping liquid solutions comprising liquid carbon dioxide) or other liquid transfer means operably connected to or associated with the drain line;
(f) a detergent formulation reservoir;
(g) a detergent formulation supply line connecting the reservoir to the carbon dioxide cleaning solution supply line or drain line; and
(h) a second high pressure pump operably connected to the detergent formulation supply line for transferring detergent formulation from the detergent formulation reservoir into the carbon dioxide cleaning solution under turbulent conditions.
An advantage of this apparatus is that it provides for the introduction of detergent formulations and the like under turbulent conditions, which facilitates the mixing of the formulations with the liquid carbon dioxide wash solution. Such a manner of introduction is particularly advantageous when the detergent formulation is immiscible, wholly or in part, with the liquid carbon dioxide wash solution.
A fourth aspect of the present invention is a method for the addition of aqueous detergent formulations and the like to a carbon dioxide dry cleaning system under turbulent conditions. The method may be carried out with an apparatus as described immediately above. The method comprises:
(a) providing a carbon dioxide cleaning apparatus comprising a wash vessel and a filter;
(b) pumping a continuous stream of liquid carbon dioxide cleaning solution from the wash vessel through the filter and back to the wash vessel to clean articles in the wash vessel; and
(c) adding a detergent formulation into the continuous stream of liquid carbon dioxide (for example, at a point downstream of the filter and upstream of the wash vessel) to introduce the detergent formulation into the continuous stream, with the detergent formulation comprising (i) at least 10 or preferably at least 20 percent water, and (ii) at least 1 percent surfactant, so that water in the detergent formulation is dispersed in the liquid carbon dioxide prior to entry into the wash vessel, without depletion in the filter.
The systems described above may be provided independently on a cleaning apparatus, or may be combined together on a cleaning apparatus to provide the capability of both manners of detergent introduction.